Due to government regulations mandating increasingly higher mileage standards for vehicles manufacturers of internal combustion engines explore every avenue to increase the efficiency of the engine to improve the vehicle mileage characteristics.
Internal combustion engine efficiency is determined by a number of engine factors, such as compression ratios, speed of operation, number of valves in each cylinder, spark plug placement, combustion chamber configuration, etc., and one of the very significant factors affecting engine efficiency is the extent of the friction resulting from relatively movable components. Friction is also usually directed to weight characteristics and engine efficiency is increased as friction and weight factors are reduced.
The engine valve train components for operating the cylinder valves are relatively complex, numerous, and a source of considerable energy loss due to friction. The energy required to operate the valve train has sought to be reduced by lowering the weight of the valve train rocker arm, and relatively thin wall rocker arm constructions have been proposed wherein the rocker arm is formed of sheet metal as typically shown in U.S. Pat. Nos. 2,176,083; 2,338,726 and 3,142,357. Friction forces can also be reduced by using roller members mounted on the rocker arm for engaging the valve train as shown in U.S. Pat. Nos. 2,176,083 and 4,182,290.
As valve train rocker arms are exposed to significant pivoting forces by the camshaft or push rod actuator displaced by the camshaft it is known to use anti-friction bearings, such as ball or roller bearings, to support the rocker arm or rocker arm mounted mechanism associated with the cam, and typical proposals are shown in U.S. Pat. Nos. 4,497,307; 4,697,473 and 4,718,379 wherein frictional forces are reduced by the use of anti-friction bearings.
Sheet metal rocker arm constructions do not readily accept antifriction bearings, are not rigid, and present rocker arm fabrication and manufacture has not eliminated all of the energy wasting and frictional loss from the valve train system. Improvements in the operating characteristics of a valve train can result in one or two miles per gallon in vehicle ratings.
It is an object of the invention to provide a valve train rocker arm of a rigid lightweight cast metal construction utilizing primary anti-friction support bearings and having a configuration providing a high strength and stiffness in combination with low weight.
Another object of the invention is to provide a rocker arm for internal combustion engines wherein the rocker arm is formed of a cast metal having substantially parallel or tapered side flanges and wherein the flanges are interconnected by homogeneous webs, the webs and side flanges together forming a high strength box or channel configuration permitting the forming of a lightweight rocker arm with a minimum of material.
In the practice of the invention the valve train rocker arm is formed by a casting method, such as investment casting or by sand casting. The rocker arm body consists of a pair of substantially parallel lateral side flanges each having a central region and ends. The flanges are the mirror image of each other, of an elongated configuration, and the portion of the body between the central region and one end constitutes a valve engaging arm while the opposite region constitutes an actuator engaging arm.
Centrally, the side flanges are formed with coaxial openings for receiving anti-friction ball bearings which are mounted upon the rocker arm support structure, and the bifurcated terminal end of the valve engaging arms preferably receives a valve train engaging anti-friction roller or bearing, while the opposite end of the rocker arm body includes a thrust bearing recess engaging the end of an actuator push rod operated by the engine camshaft.
The side flanges are relatively thin in dimension in a direction transverse to the plane of rocker arm operative movement, while the side flange dimension in the direction of plane movement is sufficiently high to resist bending and deflection during rocker arm operation. Homogeneous webs interconnect the side flanges, and a pair of spaced webs located intermediate the flanges central region and the end of the valve engaging arms whereby the resulting box cross-section configuration or the channel cross-section configuration used with investment casting or a poured casting provides a high strength interconnection between the side flanges with the addition of little weight.
Primary anti-friction bearings located in the side flanges at the central region thereof provide low friction support of the rocker arm during movement, and in the preferred construction an anti-friction roller located at the bifurcated end of the flanges the valve train.